1. Field of the Invention
The present invention relates generally to a system for controlling ignition in an internal combustion engine, and more particularly, to a system configured to produce repetitive spark for ignition having secondary current feedback to trigger start of a recharge event.
2. Description of the Related Art
There has been much investigation in the ignition art directed to systems for generating multiple spark events during combustion. Such systems are sometimes referred to as xe2x80x9cmultichargexe2x80x9d systems. Such ignition systems provide a succession of spark breakdowns to ensure ignition of a combustible air/fuel mixture introduced into a cylinder of an internal combustion engine, as seen by reference to U.S. Pat. No. 5,014,676 issued to Boyer. Boyer discloses a system configured to provide a series of sparks to increase the number of ignition events and hence the probability of combustion of the air/fuel mixture by extending the time and total energy available for combustion. Boyer discloses an ignition coil that undergoes an initial charge (i.e., initial dwell) wherein a primary current is established in a primary winding of the ignition coil. The initial dwell is immediately followed by an initial discharge of the ignition coil wherein a secondary current in a secondary winding thereof discharges through a spark plug to generate a first spark. Subsequent recharge intervals (i.e., subsequent dwell periods) follow, accompanied by respective discharge intervals (i.e., spark events). The number of sparks produced is generally determined by a predetermined operating strategy (e.g., a fixed number of sparks, or, the greatest number of sparks that can be initiated before the end of a predetermined angle of engine rotation). In addition, the period of time in conventional systems allowed for the discharge of the coil (i.e., spark event) and burn before the next recharge is determined solely based on time. However, prior approaches such as the system disclosed in Boyer have shortcomings.
One shortcoming involves the great variability in the amount of energy pulled from the coil and delivered to the combustion chamber in a given amount of time (i.e., the discharge time in fixed-time discharge systems). Uneven energy delivery may adversely affect consistency in ignition.
There is therefore a need to provide an ignition control system for producing repetitive spark in a combustion chamber of an internal combustion engine that minimizes or eliminates one or more of the shortcomings as set forth above.
An ignition system in accordance with the present invention is characterized by the features specified in claim 1.
One object of the present invention is to provide an ignition system suitable for use in generating repetitive spark that minimizes or eliminates the variability in the amount of energy delivered to the combustion chamber.
These and other objects, advantages, and features of the present invention are realized by an ignition system in accordance with the present invention. One advantage of the present invention is that the recharge interval portion of multicharge operation (i.e., repetitive spark during the firing of one cylinder) is triggered when a predetermined amount of energy has been delivered to the chamber, as determined by a secondary current sensing circuit. This improves consistency in ignition.
An ignition system in accordance with the present invention is configured for use with an internal combustion engine. The ignition system includes an ignition coil having a primary winding and a secondary winding that is coupled to a spark plug in a combustion chamber of the engine. The system further includes a switch responsive to an ignition control signal for causing a primary current to flow through the primary winding circuit. The system also includes a control circuit, which is configured to generate the ignition control signal so as to repetitively interrupt the primary current, creating pulses of secondary current to produce a plurality of sparks at the spark plug. The ignition system further includes a sensing circuit in sensing relation with the secondary winding configured to generate a secondary current signal representative of a level of secondary current in the secondary winding. Advantageously, the control circuit is further configured to generate the ignition control signal so as to reestablish the primary current in preparation of the next spark when the secondary current reaches (i.e., decays to) a secondary current threshold.
Other objects, features, and advantages of the present invention will become apparent to one skilled in the art from the following detailed description and accompanying drawings illustrating features of this invention by way of example, but not by way of limitation.